[es6] Implement inner scope for functions with destructuring

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 40863800e492da1c8983ed4015e0cc3b2339b0a1..9f913450abd9f7f8622ef1b85082bd4c3e43a15b 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -280,14 +280,13 @@ class Scope: public ZoneObject {
   bool is_block_scope() const { return scope_type_ == BLOCK_SCOPE; }
   bool is_with_scope() const { return scope_type_ == WITH_SCOPE; }
   bool is_arrow_scope() const { return scope_type_ == ARROW_SCOPE; }
-  bool is_declaration_scope() const {
-    return is_eval_scope() || is_function_scope() ||
-        is_module_scope() || is_script_scope();
-  }
+  bool is_declaration_scope() const { return is_declaration_scope_; }
   bool is_strict_eval_scope() const {
     return is_eval_scope() && is_strict(language_mode_);
   }
 
+  void set_is_declaration_scope() { is_declaration_scope_ = true; }
+
   // Information about which scopes calls eval.
   bool calls_eval() const { return scope_calls_eval_; }
   bool calls_sloppy_eval() {
@@ -614,6 +613,9 @@ class Scope: public ZoneObject {
   // constructed based on a serialized scope info or a catch context).
   bool already_resolved_;
 
+  // True if it holds 'var' declarations.
+  bool is_declaration_scope_;
+
   // Computed as variables are declared.
   int num_var_or_const_;